The invention relates to a gas duct or pipeline for conveying explosive gases or gas mixtures comprising an explosive gas as a component thereof. The present invention particularly relates to pipelines for installations supplied during operation alternately with combustible gases, and with oxygen-containing gases, and including equipment capable of gas ignition within the pipe of the gas pipeline.
In principle, whenever an explosive gas being conducted through a pipeline comes in contact with an oxygen-containing gas, or whenever a gas mixture having an explosive component is conducted through a pipeline, there exists the danger of an explosion of the gas, when the pipeline supplies an installation including equipment capable of discharging an igniting spark. Such danger exists particularly when the installation supplied by the pipeline is of the type which must be supplied alternately with different gases or gas mixtures through the same pipeline. An example of such an installation is a regenerative coke oven, which is heated with coal gas, and which is alternately charged at regular intervals with fuel gas and air. Such an installation is alternately supplied with coke oven gas and with decarbonizing air.
While the supply is changed from coke oven gas to decarbonizing air, or from air to the coke oven gas, a gas mixture containing both of these components is formed in the gas pipeline. Therefore, under certain conditions, namely an ignition, the two components exhibit the tendency to chemically react with the possible result being an explosion or detonation.
In order to avoid or reduce the danger of an explosion, the velocity of gas flow is ordinarily selected such that at the full power output of the supplied installation, a turbulent flow prevails in the pipelines and explosive gas mixtures thus appear only within a short length of the pipeline. However, in addition to the above mentioned full power output operation of the installation, there regularly appear further operational conditions, e.g., the heating-up phase of the coke oven installation or the operation thereof at throttled output, during which the velocity of flow in the gas pipelines must be reduced. However, such reduced flow velocities lead to the formation of a laminar condition of flow which leads to zones permitting mixing of the separate gas components, such zones extending through relatively long portions of the gas pipelines. Such long transition zones represent a considerable safety risk, since the danger of explosion in such long zones is substantially great, and since it is possible that once the explosion occurs, it may be propagated for a great distance within the gas pipeline, so that the destruction caused by the explosion assumes a corresponding considerable extent.
In the case of the coke oven installation mentioned above as a specific example, the initial ignition device which triggers the explosion consists of the burner head which is heated at least to the temperature of ignition.